Direct carbon-13 nuclear magnetic resonance (nmr) provides a convenient and facile method for studying the biosynthetic origin of complex natural products. Extension of methods previously developed will profice insight into the nature of the intermediates involved in the formation of complex natural products. NMR of metabolites derived from easily available 13C-enriched substrates, notably 1,2-13C sodium acetate coupled with the useful techniques of continuous wave and proton noise decoupling and mass spectrometry allows quantitative and qualitative determination of isotope enrichment at specific carbon atoms without recourse to extensive chemical degradation.